1. Field of the Invention
The invention disclosed herein relates generally to method and apparatus for material processing for thin film deposition or ion implantation applying beam-scanning technologies. More particularly, this invention relates to an improved scanning apparatus and method applied to highly uniform thin film depositions on substrates with materials sputtered from targets by collisions with energetic ion beams. The same method can be applied to other processes that need high uniformity, such as ion implantation, magnetic device manufacturing.
2. Descriptions of the Prior Art
Difficulties due to stringent uniformity requirements for advanced technology development have been encountered by those of ordinary skill in the art for applying conventional apparatuses and methods to carry out the tasks of deposition or implantation processes on substrates. These processes may also include thin film depositions for fabricating a DWDM (Dense Wavelength Division Multiplexing) filter. A specific difficulty is to deposit a thin film for manufacturing a narrow band optical filter that requires thin films with highly uniform thickness. Even though the uniformity of thin-film thickness is very critical for the narrow band optical filter, a high degree of thin-film uniformity is not easily achievable. The difficulty of unable to provide thin film with required uniformity causes low deposition yield and high manufacturing cost. New DWDM technology development demands to further reduce the bandwidth of filters for increasing the data transmitting capacity. This trends to drive more stringent requirements in thickness uniformity for achieving new filter performance and maintaining the fabrication yield. For example, the wavelength bandwidth of a 100 GHz DWDM filter is about 0.8 nm, and a 0.05% of thickness non-uniformity is required for fabricating 100 GHz filters in the area. A further reduction of the wavelength bandwidth to 0.4 nm for 50 GHz filters will require a non-uniformity of 0.02% for a DWDM filter. Many methods and apparatuses have been employed to increase the uniformity in the processes of optical coatings, ion implantation, and other applications.
A typical sputtering deposition system for the optical coatings contains a vacuum chamber where target materials are impacted by ion beams or heated by electron beams to sputter or evaporate the target materials off the targets. The materials from the targets are deposited onto substrates to form thin films. The conventional apparatus can be applied to thin film deposition on a single substrate or multiple substrates. A typical single substrate deposition system has a rotational carrier to rotate the single substrate around the substrate center axis while the target materials are sputtering onto the surface of the substrate to form the thin films. In a multiple substrate deposition system, substrates are mounted on a common rotational carrier that rotates around a central axis. Each substrate may or may not rotate along its central axis in order to increase the film deposition uniformity. In the conventional methods, the in-situ measurement of the deposition thickness is performed on a fixed radius of the rotating substrate. The high uniformity area of the rotating substrate is usually located at the fixed radius in a ring since the particle beam flux seldom changes at the fixed radius during one substrate rotation period. The width of the uniform ring depends on the size of the incident sputtered particle beam and particle beam flux distribution within the beam. Since the particle beam distribution varies over time and the deposition time is usually as long as one or two days, it is difficult to maintain the uniform deposition over a large area.
Apparatus of thickness control by introducing additional linear transverse movement to the rotation substrates in optical coating systems is disclosed in U.S. Pat. No. 5,879,519. A similar approach in ion implantation is disclosed in U.S. Pat. No. 3,778,626 in 1972. In U.S. Pat. No. 5,879,519 the magnetron deposition devices are adapted for relative movement generally transverse to the axis of rotation of the substrate carrier disk at a velocity proportional to the radial position. In this approach, the deposited area on substrates would be increased in a comparison of deposition with stationary source(s). However, this method cannot provide good thickness uniformity on the substrates because the radial transverse velocity should be inversely proportional to the radial position as disclosed in U.S. Pat. No. 3,778,626. However, the approach disclosed in U.S. Pat. No. 3,778,626 imposes three stringent requirements on deposition systems. Specifically, these requirements are 1) relative transverse movement between the deposition source and substrate has to be along radial direction with very small deviation allowed, 2) highly symmetric source particle flux profile, and 3) the distance between the carry disk center and the symmetric axis of the deposition particle flux must be very accurately determined. Also, the tolerances of these aspects are much tighter as the diameter of the carrying disk is decreased. These requirements impose tremendous practical difficulties in obtaining the deposition non-uniformity bellow 0.05%.
In a conventional ion implantation technology, a typical ion implanter is used which contains a vacuum chamber where an ion beam is generated. The ion beam impacts on a batch of wafers. In the batch system, a disk holds several wafers on its periphery. The disk rotates about its center axis. The ion beam scans along transverse direction to the disk surface at a velocity inversely proportional to the distance of the center of the disk to the beam spot. Therefore, since the wafer holder is rotating at a high speed, the ion beam was supposed to scan uniformly over annular areas with a same beam scan radius. The details of this operation are disclosed in U.S. Pat. No. 3,778,626. The approach would improve the implant non-uniformity down to 1%. However, it is difficult for further improvement of uniformity with this approach. First, the beam scan velocity is hard to be determined since distance of the disk center to the reference point of the beam spot is difficult to be practically determined. Secondly, the ion concentration profile within the source beam is normally asymmetric. A radial scan of an asymmetric ion beam still limits the achievement of a high degree of process uniformity.
For other process technologies in semiconductor and magnetic data storage device manufacturing, such as physical vapor deposition, chemical vapor deposition, reactive ion etching, electroplating, the controllable process non-uniformity is above 2%. The processes offered by these techniques are not able to meet the thickness uniformity requirements for making the narrow band optical filters.
For the above reasons, as more stringent requirements for advanced optical filters are imposed on the thickness-uniformity, the conventional methods of deposition are often unable to satisfy a reduced tolerance limit of the film-thickness variances. Furthermore, a technique to monitor and control the deposition process to achieve a predefined requirement of thickness uniformity is not available. The state of the art in film deposition technology thus limits a person of ordinary skill in the art to achieve higher thickness uniformity when systems and methods currently available are applied to carry out the thin-film deposition processes. Therefore, a need still exists in the art of process technology to provide a new and improved apparatus and method for improving the process uniformity.
It is the object of the present invention to provide a new system configuration and method for carrying out a process by monitoring and more precisely controlling the motion of the substrate(s) for process uniformity improvement. Specifically, it is the object of the present invention to present a new system configuration of thin film deposition by moving the substrate(s) in rotational and laterally reciprocated movements. The range of the lateral movement covers from one side of the substrate holder edge to at least passing the substrate holder center or to the other side of the substrate holder. The velocity of the lateral movement is inversely proportional to the distance from a reference point at or near the center of the substrate holder to any reference point near the particle source beam spot (preferably the center of the beam). With the new and improved system configuration and method of operations, the difficulties of the prior art systems and methods are resolved. More uniform thin films can be produced for optical filter manufacturing, IC (Integrated Circuit) device manufacturing, and other process manufacturing requiring high uniformity over the substrate surfaces.
A process apparatus and control method of beam scanning for achieving a very high degree of uniformity over a substrate surface are disclosed in this invention. The method includes a step of providing a vacuum chamber for containing a mechanism of generating a particle source either for thin-film deposition or other surface modification processes such as ion implantation on a single substrate or multiple substrates. The method further includes a step of containing a substrate holder (or disk) that rotates at a high speed about its center axis in the vacuum chamber. The disk holds a substrate or multiple substrates having the substrate surface(s) facing the particle source. And, the method further includes a step of providing a laterally reciprocated moving means for laterally moving the substrate holder and controlling the velocity of the lateral movement for controlling a process uniformity of said process on the substrate(s). The laterally reciprocated movement of a substrate holder can be preferably achieved by either a linear transverse motion or by a swing motion along an arc trace, or by a trace with a controllable mechanism. The velocity of the lateral movement of the substrate holder is inversely proportional to the distance between the rotation center of the substrate holder and any reference point within a projection volume generated by the particle source beam. The preferable reference point is within a cross sectional area defined by the projection volume of the particle source beam intersected by the substrate holder. The range of the lateral movement can cover at least one half of the area of the substrate holder extended from an edge to any point passing through the center of the holder, preferably from one edge to an opposite edge of the substrate holder.
A preferred embodiment of this invention discloses a thin film deposition apparatus for performing a thin-film deposition on a substrate or multiple substrates mounted on a substrate holder. The apparatus includes a vacuum chamber containing a thin-film particle source or multiple sources for generating thin-film particles to deposit a thin-film or multiple layers of thin films on the substrate(s). The apparatus further includes a substrate holder disposed in the vacuum chamber for holding the substrate(s) having a thin-film depositing surface facing the thin-film particle sources. The apparatus further includes a rotational means for rotating the substrate holder to rotate the substrate exposed to the thin-film particles for depositing a thin film thereon. The apparatus further includes a lateral moving means for laterally transversely moving or swinging the rotating substrate holder and controlling the velocity of the lateral movement inversely proportional to the distance from the rotating center of the substrate holder to a reference point in the projection area of some particle beam on the substrate surface moving plane. The extent of the lateral movement is wide enough so that the source beam can relatively scan from one side of the substrate holder to the other side.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed descriptions of the preferred embodiment that is illustrated in the various drawing figures.